1. Field of the Invention
The invention relates to display technology. More specifically, the invention relates to signs having multiple, alternating, display screens.
2. Description of the Prior Art
Electromechanical signs having the ability to present display at least two or more images through means of a number of sequentially rotating elements sign are generally well known. Examples of such signs are shown in U.S. Pat. Nos. 4,528,763, 4,002,022, and 3,921,321.
Each of the aforementioned signs includes a number of tri-lateral display elements, with each side of the element provided with a portion of an image that is displayed when all element sides having portions of the image are turned outwardly at the same time. The elements are continuously or intermittently rotated so that second and third sides of each display element yield second and third images for display.
Each of the aforementioned patents deals with particular problems and solutions of providing such signs. For example, U.S. Pat. No. 4,528,763 ('763) deals with provision of trilateral screen assemblies and a system for easily providing the tri-lateral assembly onto holding assemblies for rotation. U.S. Pat. No. 4,002,022 ('022) illustrates various mechanisms for rotating tri-lateral elements in such a sign. U.S. Pat. No. 3,921,321 ('321) illustrates a mechanism for intermittent rotation comprising a Maltese cross and gear arrangement.
The '022 and '321 patents illustrate rather cumbersome means for rotating the display elements. In order to increase reliability and decrease manufacturing costs, the more basic the mechanism utilized to rotate such constituent elements, the more cost effective such sign will be to manufacture.
Another important feature provided in certain signs of this type is illumination of the display elements. Such illumination may comprise a light source directed at the face of the display or backlighting of the elements through transparent or semi-transparent display images. Shown in U.S. Pat. No. 4,381,616, is a light source comprising a fluorescent tube positioned within each of the tri-lateral display elements, which rotates or remains stationary with the element and is co-axial the axis of rotation of the display element. The '616 patent emphasizes provision of opaque edge members on each of the panels to prevent the light source from degrading the quality of the display image. However, in a system such as shown in the '616 patent, the light sources are difficult to replace. In particular, the display elements must be removed from their mounting and the light source slid out of the element.
A second sign system of this type is the Graphic Revolutions.RTM. sequential-image transparency illuminator, manufactured by Clearr Corporation, Minneapolis, Minn. The Graphic Revolutions.RTM. provides a back-lit display unit requiring display images comprised of transparencies to be affixed to the sides of the display elements, and utilizes 5,000.degree. Kelvin, color correct lamps for illumination of the transparencies. The advantage of such fluorescent lamps is that they provide an even illumination over the entire vertical and horizontal surface area of the sign. However, as noted above, such lamps are rather difficult to replace. In addition, the Clearr Corporation sign utilizes special transparencies manufactured from a translucent acrylic material affixed to the rotatable elements, which can increase the cost of use for the sign.